AB0793 SERUM C3 LEVELS ARE ASSOCIATED WITH DISEASE PATHOLOGY IN MICROSCOPIC POLYANGIITIS: RESULTS FROM THE REVEAL COHORT
Authors: R. Watanabe, T. Gon, S. Matsuda, A. Okazaki, A. Manabe, M. Shoji, K. Kadoba, W. Yamamoto, R. Hiwa, T. Kotani, M. Hashimoto
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Recent studies have shown that complement C5a receptor antagonist is highly effective for treating microscopic polyangiitis (MPA), suggesting that complement is substantially involved in the pathogenesis. <h3>Objectives</h3> In this study, we aimed to examine whether serum C3 levels were associated with clinical characteristics, disease severity, treatment, and prognosis in the Japanese multicenter cohort. <h3>Methods</h3> Patients with MPA whose C3 levels were measured at diagnosis were enrolled. The diagnosis of MPA was based on the 2012 revised Chapel Hill consensus criteria. Patients were divided into three groups: low C3 (&lt;86 mg/dL), normal C3 (86-130 mg/dL), and high C3 (&gt;130 mg/dL) groups to compare clinical characteristics. Analysis of variance or the Kruskal–Wallis test was used when the variates were numeric, while the chi-squared test or Fisher's exact test was used when variates were categorical. <h3>Results</h3> A total of 158 patients (low C3: 28, normal C3: 90, high C3: 40 patients) were enrolled. Baseline characteristics did not differ between the three groups in age at onset, sex, smoking history, and MPO-ANCA positivity. Serum C3 levels (P&lt;0.001) as well as C4 (P&lt;0.001) and CH50 levels (P=0.0013) were significantly lower in the low C3 group. In addition, hemoglobin (P=0.0058), platelets (P&lt;0.001), and serum CRP levels (P=0.002) were significantly lower in the low C3 group, while serum creatinine levels (P=0.001), BVAS (P=0.039), and five factor scores (P=0.005) were significantly higher in the low C3 group. Notably, the proportion of patients who fulfilled the 2022 revised ACR/EULAR classification criteria for MPA was significantly lower in the low C3 group (P=0.039). Initial prednisolone dose and survival did not differ between the three groups. <h3>Conclusion</h3> Low C3 levels are associated with severe disease and renal dysfunction, while high C3 levels are associated with elevated CRP levels. Serum C3 levels are closely associated with disease pathology. <h3>References</h3> [1]Jane DRW, Merkel PA, Schall TJ, Bekker P; ADVOCATE Study Group. Avacopan for the treatment of ANCA-Associated Vasculitis. N Engl J Med. 2021:384:599-609. <h3>Acknowledgements</h3> We would like to thank BioRender.com (https://biorender.com) for the schematic Figure. <h3>Disclosure of Interests</h3> Ryu Watanabe Speakers bureau: Asahi Kasei, Eli Lilly, Chugai, GSK, Sanofi, Grant/research support from: AbbVie, Takaho Gon: None declared, Shogo Matsuda Speakers bureau: Abbvie, Ayana Okazaki: None declared, Atsushi Manabe: None declared, Mikihito Shoji: None declared, Keiichiro Kadoba: None declared, Wataru Yamamoto: None declared, Ryosuke Hiwa: None declared, Takuya Kotani Speakers bureau: Abbvie, Bristol-Myers Squibb, Chugai, Eisai, Eli Lilly, and Pfizer, Motomu Hashimoto Speakers bureau: Eli Lilly, Chugai, Tanabe-Mitsubishi, Bristol Myers Squibb, Esai, Grant/research support from: AbbVie, Asahi Kasei Pharma, Astellas, Bristol Myers Squibb, Esai, Daiichi Sankyo, Eli Lilly, Novartis.